The Geochemical Features of Au-Ag Epithermal Mineralization at the Kayenmyvaam Volcanic Uplift, Central Chukotka

Abstract

This paper considers geochemical features of the Au-Ag epithermal mineralization at the Kayenmyvaam volcanic uplift (KVU) situated in the middle of the Chukchi segment which is part of the inner zone of the Okhotsk–Chukchi volcanogenic belt (OChVB). New evidence is presented concerning the composition and concentrations of trace elements, including REEs, in the ores of Au-Ag deposits (Arykevaam, Kyaenmyvaam, and Televeem). The ores were found to be enriched in a wide range of trace elements (Li, Se, Mo, Au, Ag, As, Sb, Cu, Pb, In, Cd, Tl, Zn, Bi, Te, and W). The enrichment ratios vary between a few times (Li, Se, Bi, Zn, Tl, In) to tens (Mo, Te, Pb, Cd), hundreds (As, Cu), thousands and tens of thousand times (Au, Ag, Sb). Comparative analysis of the distribution patterns of trace elements shows synchronous enrichment of the ores in similar sets of trace elements. The ores were found to be dominated by light “hydrophile” lanthanoids of the “cerium” group, slightly inclined near-chondrite patterns, without obvious europium maxima and minima, which have configurations similar to the REE patterns of volcanic rock sequences of the andesite–diorite series. The ore-forming fluids belonged to an NaCl–H₂O hydrothermal system enriched in Cl relative to F; the Y/Ho ratios in the ores correspond with the range of ratios characteristic for present-day hydrothermal fluids in the backarc basins. The low Co/Ni ratios in the ores probably reflect a large involvement of meteoric near-surface fluids in the mineralization. The Ce/Ce* and Eu/Eu* ratios vary between slightly negative to moderately positive values (Ce/Ce* between 0.71 and 1.07) and (Eu/Eu* between 0.63 and 1.14). This combination of Ce/Ce* and Eu/Eu* corresponds to oxidizing conditions that were existent during the mineralization. The geochemical data indicate andesitic magmas and meteoric waters as the most likely sources of the fluids. The results classify the mineralization under study as belonging to the high sulfidation epithermal class.